A necessary and sufficient condition for the representation of a function as a Hankel-Stieltjes transform F. Cholewinski; D. Haimo; A. Nussbaum — 1970 Studia Mathematica
Extension of Positive Definite Functions and Representation of Functions in Terms of Spherical Functions in Symmetrie Spaces of Noncompact Type of Rank l. A. Edward Nussbaum — 1975 Mathematische Annalen